This invention relates to a method and apparatus for separating two immiscible liquids, for example, kitchen effluent contains a mixture of grease, water and solids.
Kitchen effluent generated during food processing has conventionally been collected in a grease trap separator, which is commonly a rectangular tank made of pre-cast concrete, buried below grade. In the separator, the grease, being of a lower density than the water, rises to the top, forming a separate grease mat layer. Periodically, the grease is removed from the trap, normally with a vacuum pump. The grease may then be disposed of in a landfill or sold to rendering companies for conversion into useful products.
Processing of the grease into useful products is obviously preferred to dumping of the grease into a landfill, which also may not be possible due to the increased environmental regulations. Processors, however, are not always willing to accept grease if it includes a significant percentage of water, i.e., more than fifteen percent (15%), because of the increased difficulty in processing. Moreover, the prolonged contact of water with the grease tends to make the grease rancid as a result of the breakdown of lipids into shorter chain fatty acids, decreasing the value of the grease.
The prior art discloses various methods and apparatus for separating two immiscible liquids, and also discloses various methods and apparatus for removing one liquid from contact with the other after separation of liquids into two layers in a separator. For example, in some cases, the lighter liquid is discharged by gravity from the separator through an upper pipe and the heavier liquid is discharged from the separator through a lower pipe. Generally, the methods and apparatus relate to the separation of grease or oil from water.
U.S. Pat. No. 2,747,736 to Mobley describes a device for removing grease from wastewater in a separator, in which grease which floats to the top of the separator is removed by hydrostatic forces. The grease is then stored at a collecting and storage point remote from the separator.
U.S. Pat. No. 5,236,585 to Sink describes an apparatus comprised of a separator in which oil and water are separated. The oil, which floats to the top of the water, flows under gravity to a second separator, where remaining oil is removed, e.g., by filtration. Water is removed from the bottom of the first separator.
Other patents show similar devices. U.S. Pat. No. 4,915,823 to Hall, describes a device for separating oil from water in bilge discharges. After separation, the oil and water are removed through separate discharge pipes. U.S. Pat. No. 4,119,541 to Makaya, discloses a similar arrangement for cleaning up oil spills by separating oil from seawater. U.S. Pat. No. 4,400,274 to Protos, describes a gravity separator in which solids are removed prior to separation of the grease and water. Those systems often suffer the problem of incomplete removal of grease from the water, leading to waste of recyclable grease, and perhaps more importantly, the need to treat the water more thoroughly because of the residual grease contaminants.
The kinds of apparatus disclosed in the prior art, however, are not readily adaptable for use with the thousands of conventional grease traps that currently exist. Since these traps are generally comprised of a concrete storage tank buried several feet below ground level, i.e., grade, which has a pair of generally cylindrical access ports fitted with manhole covers, removal or structural modification is difficult. An apparatus which would permit removal of grease from water with great efficiency in conventional grease traps would be of substantial commercial utility.
Further, there is a need in the art for a new apparatus for separation of oil/grease from wastewater which is simple in design so that service is not often needed, yet capable of being done in the field by simple replacement of easily replaceable parts.